Add macros, declarative handlers (defhandler), and convert all fragment routes to sx

Phase 1 — Macros: defmacro + quasiquote syntax (`, ,, ,@) in parser,
evaluator, HTML renderer, and JS mirror. Macro type, expansion, and
round-trip serialization.

Phase 2 — Expanded primitives: app-url, url-for, asset-url, config,
format-date, parse-int (pure); service, request-arg, request-path,
nav-tree, get-children (I/O); jinja-global, relations-from (pure).
Updated _io_service to accept (service "registry-name" "method" :kwargs)
with auto kebab→snake conversion. DTO-to-dict now expands datetime fields
into year/month/day convenience keys. Tuple returns converted to lists.

Phase 3 — Declarative handlers: HandlerDef type, defhandler special form,
handler registry (service → name → HandlerDef), async evaluator+renderer
(async_eval.py) that awaits I/O primitives inline within control flow.
Handler loading from .sx files, execute_handler, blueprint factory.

Phase 4 — Convert all fragment routes: 13 Python fragment handlers across
8 services replaced with declarative .sx handler files. All routes.py
simplified to uniform sx dispatch pattern. Two Jinja HTML handlers
(events/container-cards, events/account-page) kept as Python.

New files: shared/sx/async_eval.py, shared/sx/handlers.py,
shared/sx/tests/test_handlers.py, plus 13 handler .sx files under
{service}/sx/handlers/. MarketService.product_by_slug() added.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

relations/bp/fragments/routes.py

@@ -1,21 +1,23 @@
 """Relations app fragment endpoints.
 
-Generic container-nav fragment that renders navigation items for all
-related entities, driven by the relation registry.
+Exposes sx fragments at ``/internal/fragments/<type>`` for consumption
+by other coop apps via the fragment client.
+
+All handlers are defined declaratively in .sx files under
+``relations/sx/handlers/`` and dispatched via the sx handler registry.
 """
 
 from __future__ import annotations
 
-from quart import Blueprint, Response, g, request
+from quart import Blueprint, Response, request
 
 from shared.infrastructure.fragments import FRAGMENT_HEADER
+from shared.sx.handlers import get_handler, execute_handler
 
 
 def register():
     bp = Blueprint("fragments", __name__, url_prefix="/internal/fragments")
 
-    _handlers: dict[str, object] = {}
-
     @bp.before_request
     async def _require_fragment_header():
         if not request.headers.get(FRAGMENT_HEADER):
@@ -23,70 +25,12 @@ def register():
 
     @bp.get("/<fragment_type>")
     async def get_fragment(fragment_type: str):
-        handler = _handlers.get(fragment_type)
-        if handler is None:
-            return Response("", status=200, content_type="text/sx")
-        src = await handler()
-        return Response(src, status=200, content_type="text/sx")
-
-    # --- generic container-nav fragment ----------------------------------------
-
-    async def _container_nav_handler():
-        from shared.sx.helpers import sx_call
-        from shared.sx.relations import relations_from
-        from shared.services.relationships import get_children
-        from shared.infrastructure.urls import events_url, market_url
-
-        _SERVICE_URL = {
-            "calendar": events_url,
-            "market": market_url,
-        }
-
-        container_type = request.args.get("container_type", "page")
-        container_id = int(request.args.get("container_id", 0))
-        post_slug = request.args.get("post_slug", "")
-        nav_class = request.args.get("nav_class", "")
-        exclude_raw = request.args.get("exclude", "")
-        exclude = set(exclude_raw.split(",")) if exclude_raw else set()
-
-        nav_defs = [
-            d for d in relations_from(container_type)
-            if d.nav != "hidden" and d.name not in exclude
-        ]
-
-        if not nav_defs:
-            return ""
-
-        parts = []
-        for defn in nav_defs:
-            children = await get_children(
-                g.s,
-                parent_type=container_type,
-                parent_id=container_id,
-                child_type=defn.to_type,
-                relation_type=defn.name,
+        handler_def = get_handler("relations", fragment_type)
+        if handler_def is not None:
+            result = await execute_handler(
+                handler_def, "relations", args=dict(request.args),
             )
-            for child in children:
-                slug = (child.metadata_ or {}).get("slug", "")
-                if not slug:
-                    continue
-                if post_slug:
-                    path = f"/{post_slug}/{slug}/"
-                else:
-                    path = f"/{slug}/"
-                url_fn = _SERVICE_URL.get(defn.to_type)
-                href = url_fn(path) if url_fn else path
-                parts.append(sx_call("relation-nav",
-                    href=href,
-                    name=child.label or "",
-                    icon=defn.nav_icon or "",
-                    nav_class=nav_class,
-                    relation_type=defn.name))
-
-        if not parts:
-            return ""
-        return "(<> " + " ".join(parts) + ")"
-
-    _handlers["container-nav"] = _container_nav_handler
+            return Response(result, status=200, content_type="text/sx")
+        return Response("", status=200, content_type="text/sx")
 
     return bp